One of the most confusing topics for my General Class students is the dB. I can understand why they’re confused. First of all, it’s an expression of a ratio, not an absolute unit. Second, it’s logarithmic, not linear. Third, there are a number of different units that are called dB: dB, dBm, dBV, etc.
AudioDesignLine.Com has started a series of articles excerpted from the book, Sound System Engineering, that attempts to the explain the decibel. The first article in the series is “Using the Decibel – Part 1: Introduction and underlying concepts.” It starts out with an interesting history of how engineers in the 1920s at Bell Labs came up with the concept of the decibel. What they were trying to do is to describe signal losses in telephone circuits.
Fortunately, for engineers–and amateur radio operators–the concept of the decibel can be applied to RF circuits and antennas, as well as telephone and audio circuits. Mastering the concept can really help you envision what’s going on in these circuits and systems.